Can a person who doesn't like to talk much still become a good lecturer?

Absolutely, a person who's not naturally inclined to be a speaker can become a good lecturer and scientist. One of my best professors, actually, was a person with such inclinations. Finding that speaking was not something that he was good at, he turned it into an object of study and began collecting heuristics about what made a good and effective talk. By studiously applying these heuristics to his own teaching and professional communication, he could at least ensure that his talks did not fail on any identifiable dimension.

Talks need to do a lot of different things at once: holding attention, identifying key salients, speaking at different levels to different parts of the audience, providing "breadcrumbs", etc. Because of this, it often turns out that it's much less important to do any aspect brilliantly than to make sure that no aspect has been neglected. This professor might not have been a brilliant and exciting comedian, like some who are natural lecturers, but he often gave better lecturers than the naturals. The more natural lecturers were often simply less consistent: following their enjoyment and intuition produced brilliance in some aspects and weaknesses in others, while his stolid application of heuristics ensured an across-the-board solidity of presentation.

In short: ultimately, it's not a matter of talent but of choices for how to invest in acquiring skills.

I used to be INCREDIBLY shy as a child / teen / young adult. I hated public speaking and did anything that I could to avoid it.

Mid 20s I ended up unemployed and was told by a family member that you don't even need to interview to be a substitute teacher, you just sign up, get a background check, and start getting work. Desperately needing money, I went for it. And they were right, I started getting work right away.

It was stressful at times but it helped me get out of my shell a lot. And not just get out of my shell, but plan and execute strategies to keep my "audience" (the kids) engaged. Because let me tell you something about teaching elementary kids... you either take command and keep the kids engaged, or you spend the whole day dealing with discipline issues instead of teaching, which is the most frustrating thing in the world. It was a trial by fire, so to speak, and I figured it out in time.

I grew to love it (went back and got a teaching degree and teach elementary computers now) but moreso I found that A. I was no longer terrified by public speaking and B. I actually kind of liked it.

So I started signing up to do presentations at various video game conferences / etc. Now I was presenting for adults but honestly... it's not that different from teaching elementary classes. Make a plan that covers the entire time period you're going to be up there. Have alternatives if your plan isn't working. Keep the audience engaged (I always plan "activities" for the audience so it isn't just me / my partners up there talking.) The vast majority of my anxieties used to come from "what if I flop in front of a crowd" and although that is always possible, good planning and audience engagement goes a long way towards minimizing that risk.

Not sure if this helps you since I don't teach adults, but I've thought about moving in that direction sometimes to pick up some extra work, like teaching night classes or whatever, and while the before-elementary-teaching me would never have even dreamed of trying to teach college classes, now it's like yeah, why not? Current me is more than prepared for that challenge.

I'm still actually somewhat shy, and at parties and stuff I'll often end up just kind of standing near the outside of a circle and listening without saying much. But now I have the skills and experience to public speak, and I feel pretty solid about doing it. Recently my 5+ year long girlfriend came to assist me for an hour long presentation (complete with activities) at a video game conference with a crowd of around 100 people and despite being in an intimate relationship with me for years and seeing how I interact with people in other situations, afterwards she told me she was shocked at how well I commanded the thing... detailed planning, speaking loud and clear, energetically running around the room, actively engaging the audience, making people laugh, etc. Apparently I become a "different person" when I'm in control of a public presentation as opposed to being just another face in a crowd.

So yeah, not sure this totally answers your question, but you can definitely go from scared, not so great public speaker to feeling generally in control and able to take command of the situation and do a great job. And though I doubt you want to start substitute teaching elementary kids, there are probably other paths too. Just getting the practice helps.

This isn't to say I don't sometimes get nervous about it though. I think some level of nerves is pretty normal.

Yes, I have known several. They may be a better "lecturer" because they will use other teaching techniques than lecturing which are more effective because they lead to active learning.